Download Respiration

Respiration
Respiration
• Respiration is a process in which organic
molecules act as a fuel
• Organic molecules are broken down in a series
of stages to release chemical potential energy,
which is used to generate ATP
• Main organic fuel for most cells is a
carbohydrate (glucose)
– Others include fatty acids, glycerol, amino acids
Respiration
• Glucose breakdown can be divided into four
stages:
1.
2.
3.
4.
Glycolysis
The link reaction
The Krebs cycle
Oxidative phosphorylation
The glycolytic pathway
• Glycolysis is the splitting, or lysis, of glucose
• 6 carbon glucose split into 3 carbon pyruvate
• Energy is needed in first steps but released in
later steps (net gain of 2 ATP)
• Takes place in cytoplasm
Glycolysis
• First stage:
phosphorylation
– Glucose(6C) is
phosphorylated using
ATP (2 ATP/glucose)
– 2 phosphates to
glucose creates
hexose phosphate
(6C) which breaks
down into 2 triose
phosphate (3C)
Glycolysis
• Hydrogen removed from triose phosphate and
transferred to carrier molecule NAD (nicotinamide
adenine dinucleotide) to form reduced NAD (NADH)
• Each NADH molecule can be used to transfer energy
to other molecules during respiration
• The end product of glycolysis, pyruvate (3C), still
contains chemical potential energy
The link reaction
• Pyruvate passes by active transport into
mitochondrial matrix
• It is decarboxylated (CO2 is removed) and
dehydrogenated (H is removed) and combined
with coenzyme A (CoA) to form acetyl
coenzyme A (acetyl CoA)
The link reaction
• The hydrogen removed from pyruvate is
transferred to NAD to form reduced NAD
(NADH)
• Fatty acids from fat metabolism can also be
used to create acetyl CoA
The Krebs Cycle
• Aka citric acid cycle aka TCA cycle
• Closed pathway of enzyme controlled
reactions
– Acetyl CoA + oxaloacetate (4C) to form citrate (6C)
– Citrate is decarboxylated and dehydrogenated to
give off CO2 and H+ which are accepted by NAD
and FAD
– Oxaloacetate is regenerated to combine with
another acetyl CoA
The krebs cycle
• Part of the aerobic pathway, but does not use
oxygen
• Can be used in anaerobic processes like
fermentation which produces lactic acid
• Each turn of the cycle produces:
– 2 CO2 molecules
– One FADH
– Three NADH
– One ATP
Oxidative phosphorylation
• ADP to ATP come from activity of electron
transport chain
• Takes place in inner mitochondrial membrane
• NADH and FADH are passed to electron
transport chain where hydrogens are removed
and split into H+ and e• Electron is transferred to first series of
electron carriers
Oxidative phosphorylation
• As electrons are moved from carriers with
high energy to carriers with low energy,
energy is released
• Some of this energy is used to move protons
across the membrane (ATP synthase) to
generate ATP
• Net gain of 28-32 ATP
Oxidative phosphorylation
• Oxygen acts as a final electron acceptor
– Reduces oxygen to water